1. Field of the Invention
The present invention relates to an engine control device for controlling output power of the engine in accordance with an amount of the electric load of the engine.
2. Description of the Related Art
With respect to such engine control device, for example, an engine control device is proposed in Unexamined Japanese Utility Model Publication (Kokai) No. 3-47445. In the engine control device, the duty ratio of a power transistor, which controls the supply of current in the field of the alternator and a revolution speed of the engine. An output current corresponding to an amount of the electric load of the alternator is estimated based on the detected duty ratio of a power transistor and the revolution speed of the engine. An intake of gas for the engine is increased by a quantity corresponding to the load quantity of electricity by driving an actuator so that the power of the engine is increased.
Consequently, even if the load of electricity is given, a battery can be controlled to a desired voltage and reduction in the revolution speed of engine due to supply of the load can be prevented.
However, even if actual load quantity of electricity is constant in a conventional device, the duty ratio of a power transistor may be changed. This change is derived from the delay of operation of the above-mentioned power transistor and the instability of power supply.
Thus, if duty ratio is changed, it is determined as the change of the load quantity of electricity. Accordingly, the intake of the gas is changed, and hunting of the rotation of engine and life reduction of an actuator disadvantageously occur.
Conventionally, the field current is controlled to keep the voltage of a battery to a desired value. Even the voltage drop of the battery due to the external factor, for example, the temperature drop of the battery etc., the field current is increased. The intake quantity of gas is also increased by the corresponding value of increment of the field current so that the output of engine increases.
Therefore, the output of engine is sometimes increased in spite of no load supply by an operator. In this case, the operator is unnecessary worried.
Further, a determination of idling up or idling down is carried out according to the duty ratio of a power transistor in order to change a target revolution speed of engine. Therefore, the fear of the repeat of the idling up or the idling down has occurred by particular operation states. Further, the idling up or the idling down is carried out in accordance with ON/OFF of intermittent load so that the rotation of engine might become unstabilized.